Yep, I suppose BMW could program you the retrofit, but be prepared to pay quite a bit for what can be done in about 30 min
I am not experienced in doing remote programming, maybe someone from the forum could do this, however if you are computer inclined it is quite simple.
There are very good instructions on how to code the modules from the forum. All you need to do is a bit of searching
The cable can be bought on ebay and the rest is free from the internet or forum.